Recent research has demonstrated, in nonpregnant rats, that consumption of placenta or amniotic fluid significantly enhances opioid-mediated analgesia, although it does not, by itself, produce analgesia. Placenta and amniotic fluid ingestion have been shown to potentiate analgesia produced by injection of a narcotic drug (morphine), vaginal/cervical mechanical stimulation, or footshock; presumably, it also potentiates analgesia produced by elevation of endogenous opioids during delivery. The purpose of the proposed research is to isolate and characterize the placental opioid- enhancing factor (POEF). Using tail-flick latency in rats as a behavioral measure of pain threshold, the presence and potency of POEF in various fractions of rat placenta and amniotic fluid will be determined primarily by testing for enhancement of morphine- induced analgesia (3.5 mg/kg). POEF will be isolated from rat amniotic fluid and placenta, and characterized using exhaustive dialysis, ammonium sulfate precipitation, and both HPLC and column chromatographic techniques, which separate proteins and peptides by size, charge, and isoelectric point. Homogeneity will be confirmed by gel electrophoresis. An attempt will be made to produce an antibody to POEF, and to develop an immunoassay (ELISA) to facilitate the detection and quantification of POEF activity. Once some progress has been made in the isolation and purification of POEF from rat afterbirth material, bovine and human placenta will be analyzed for POEF using the rat tail-flick latency test as a behavioral assay, and using an immunoassay, if that proves feasible. Overall, this information will expand our knowledge of the physiological bases for pain, for the action of narcotic drugs, and specifically for opioid-mediated analgesia; it will also shed light on the nature of what is apparently a naturally-occurring opiate enhancer, and may provide future direction for the development of a new nonnarcotic analgesic.